Lawn and Ornamental Part 1 of 3

7/29/2019 Lawn and Ornamental Part 1 of 3

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Lawn and Ornamental Part 1 of 3

Nematode Management in Residential Lawns

IFAS Publication ENY-006

Prepared by J.C. William Crow

Learning Objectives:

To understand the unique biology of this pest

To be able to identify this pest

To understand the impact of this pest on humanity


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Nematode Management in Residential Lawns

A well-maintained lawn can help beautify our environment, reduce water runoff and

reduce water and air pollution. In 1991-92 there were 3.3 million acres of grass grown inhome lawns in Florida, making home lawns the largest agricultural crop in the sunshine

state. Just like any other crop, pest management is a key for growing healthy grass in a

home lawn. Plant-parasitic nematodes are probably the least understood and most

difficult to manage of the turfgrass pests in Florida (Figure 1).

Figure 1. Diagram of a typical plant-parasitic nematode.

What are Nematodes?

Nematodes are unsegmented roundworms, different from earthworms and other familiarworms that are segmented (annelids) or in some cases flattened and slimy (flatworms).Nematodes living in soil are very small and most can only be seen using a microscope(Figure 2). There are many kinds of nematodes found in the soil under any home lawn.Most of these are beneficial, feeding on bacteria, fungi, or other microscopic organisms.There are even nematodes that can be used as biological control organisms to helpmanage important turf insect pests. Unfortunately, there are also a group of nematodesthat feed on plants, these are called plant-parasitic nematodes (Figure 1).


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Figure 2. Size comparison of a typical plant-parasitic nematode to a cotton thread.

All plant-parasitic nematodes have a stylet or mouth-spear that is similar in structure and

function to a hypodermic needle (Figure 3). The nematode uses the stylet to puncture plant

cells, and then injectdigestive juices and ingest plant fluids through it. All of the plant-

parasitic nematodes that are important turfgrass pests feed on roots. Some plant-

parasitic nematodes remain in the soil and feed by inserting only their stylet into the

root, these are called ectoparasitic nematodes (Figure 4). Others, using their stylet to

puncture an entry hole in the root, feed with their body inside the root tissue. These are

called endoparasitic nematodes (Figure 5). Of the major nematodes that cause damage

to turfgrasses in Florida, sting, awl, stubby-root, sheath, sheathoid, and ring nematodes

are strictly ectoparasites, root-knot nematodes are strictly endoparasites, and lance

nematodes feed both endo and ectoparasitically.

. Figure 3.A typical plant-parasitic nematode styletresembles a hypodermic needle


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Figure 4.An ectoparasitic nematode feeding by inserting its stylet into a root tip.

Figure 5. Endoparasitic nematodes burrowing within a root.

How Do Nematodes Damage Grass?

As plant-parasitic nematodes feed they damage the root system and reduce the ability

of the grass to obtain water and nutrients from the soil. Roots may be abnormally shortand appear darkened or rotten when damaged by plant-parasitic nematodes (Figure 6).Root galls or knots associated with certain nematode damage to other crops are usuallynot evident on grasses. When nematode population densities get high enough, or whenenvironmental stresses such as high temperatures or drought occur, above groundsymptoms may become evident. Symptoms include yellowing, wilting, browning,thinning out, or death (Figure 7). Often weeds such as spurge, sedges, or Florida pusleybecome prominent as the grass thins out (Figures 8, 9, 10). Nematode damage usually


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occurs in irregularly shaped patches that may enlarge slowly over time (Figure 7). Beaware that similar conditions may be caused by other factors such as localized soilconditions, fungi, or insects.

Figure 6. Healthy grass roots (left) and dark, rotting grass roots damaged by nematodes.

Figure 7. Typical nematode symptoms on a lawn; irregular patches of declining grass.


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Figure 8. Spurge, a weed often associated with turf declining from nematode injury.

Figure 9. Sedge, a weed often associated with turf declining from nematode injury.


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Figure 10. Florida pusley, a weed often associated with turf declining from nematode injury.

How Do I Know if Nematodes are a Problem?

With any plant problem, having an accurate diagnosis is important to address theproblem and to avoid wasting effort and unnecessary pesticide applications. The only

reliable way to determine if plant-parasitic nematodes are involved in a grass problem isby having a nematode assay conducted by a professional nematode diagnostic lab. TheFlorida Nematode Assay Lab is such a facility and will assay nematode samples for acost that is currently $20 for each sample from Florida and $25 for each sample fromoutside of Florida. Nematode sample kits containing everything needed to collect andsubmit a sample, along with instructions, are available at your local county CooperativeExtension office.


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Figure 11. University of Florida Nematode Assay Kit.

Nematode analysis is a separate procedure and requires different sampling guidelines

than those required for soil analysis or plant disease samples. Be aware that when aplant disease sample is submitted to most labs a nematode analysis is not normallyperformed unless you specifically request it. Nematode analysis often requires separatepayment and may even be sent to a separate address. Familiarize yourself with theprocedures required by the lab where you intend to submit the sample. The accuracy ofthe diagnosis depends on the quality of the sample that you submit. If you are taking asample for submission to another lab, or if you are submitting a sample to the Universityof Florida lab without using our sample kits, following the guidelines below will helpinsure an accurate diagnosis:

1) A sample must consist of multiple soil cores. Nematodes are not evenly

distributed in soil, they congregate in hot spots. Nematode populations may behigh at one spot and low just a few feet way. Collect soil from 20 locations in thelawn. Samples should be taken 3 inches deep. About a handful of soil from eachlocation is adequate. Combine all the soil into a single plastic bag. The totalvolume of soil from the samples should be between 1 pint and a half gallon.Samples may be taken with a shovel, trowel or other device. If using a shovelyou can put part of the soil from 20 shovel fulls into a bucket. Thoroughly mix thesoil in the bucket then take out a pint for analysis.

2) If damage is evident then sample near the margin of the affected area (Figure12). Nematode populations will decline in severely damaged areas because they

have nothing left to eat. Therefore, populations tend to be highest near the edgesof a declining area where the grass is still alive. If damage is occurring in anumber of areas in one field take a few cores from the border of several affectedareas to make the 20 cores.


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Figure 12. Collect cores for a nematode sample from the edges of declining areas.

When taking samples from turf that is not showing symptoms, or if sampling beforeplanting, sample in a zig-zag pattern across the area (Figure 13).

Figure 13. When sampling healthy appearing turf, collect cores in a zig-zag pattern across the area.

3) Put the soil from each sampled area into a plastic bag and seal it. Nematodesrequire moisture to survive so drying the soil will kill them. This is different thansubmitting a sample for nutrient analysis where dry soil is preferred. Make surethat each bag is labeled with a permanent marker so that the diagnosis can be


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assigned to the correct area. If using a self-sealing bag seal it with tape alsobecause the zippers often come open in transit.

4) Handle samples carefully. Do not expose samples to direct sunlight or heat.Nematodes are sensitive to high temperatures and UV light. Leaving samples on

the dashboard or in the back of a pickup truck can kill them quickly andnegatively affect the accuracy of the diagnosis. Keeping the nematode sample ina cooler is best.

5) Submit the sample right away. Next day delivery is best. One study foundgreatest nematode recovery from hand-delivered samples, the next highest fromnext-day delivery, and the lowest from regular postal delivery.

The staff at the Florida Nematode Assay Lab will make a determination on whether or

not nematodes are a problem based on which nematodes are found and how many ofthem there are. Not all plant-parasitic nematodes are equal in their ability to harm grass.For example, one sting nematode can cause damage equal to hundreds of individualsof some other types of plant-parasitic nematodes. The number of each type ofnematode in 100 cc of soil from the sample that you submit will be compared toestablished thresholds for these nematodes (Table 1). If nematode numbers are belowthe thresholds then a statement that "Nematodes are below levels believed to bedamaging to crop indicated" will be stated on your results form. If nematode numbersexceed thresholds then a statement that "This crop is at high risk of damage caused bythe nematodes indicated" or "This crop is at moderate risk of damage caused by thenematodes indicated. Damage may occur if nematode populations increase or if the thecrop is under stressconditions," will be made.

Be aware that different diagnostic labs may use different extraction techniques, usedifferent quantities of soil, or use different thresholds. Because of this, samplessubmitted to separate labs may report different quantities of nematodes. Do not bealarmed by this, in most cases the different thresholds used are adjusted to account forthe differences in methodology and local conditions. However, if you are using a lab indistant locations, your local conditions or regional variations in nematodeaggressiveness may not be taken into account. Often your local labs will provide themost accurate assessments.

What Can I Do About Nematodes in My Lawn?Because plant-parasitic nematodes live in soil or roots, the pesticides used to kill themtend to be very toxic and are water soluble. Because of health risks and environmentalconcerns there are currently no toxic nematicides that are labeled for use on establishedhome lawns. There are a number of products available for use on home lawns that aremarketed as organic, biological or non-toxic that claim to be suppressive to plantparasitic nematodes. Be aware that in order to be labeled for home use these types of


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products need to be safe, but do not need to be proven effective. Nematologists at TheUniversity of Florida have tested many of these products for efficacy, generally withdisappointing results.

Adding soil amendments can help the grass tolerate nematode damage or possibly

suppress nematode population densities. Remember that anything that can be done toimprove root health is good. Colloidal phosphate incorporated into fine sand has beenshown to help Bermuda grass withstand attack by certain nematodes. Organic materialssuch as composted municipal sludge or manures can also promote grass health, and atthe same time may stimulate fungi that attack nematodes. Some of the best practicesfor managing nematode damage in home lawns include avoiding other stresses on thegrass. Grass that is given proper watering and fertilization can often withstand higherlevels of nematode infestation than grass suffering from drought or nutrient deficiencies

Over-fertilization should also be avoided, too much nitrogen can stimulate theproduction of succulent roots that are more susceptible to nematode damage. Grassthat is mowed too low, or that is allowed to grow too tall between mowing, is also moreprone to succumb to nematodes. Frequent mowing at moderate height is best. Whileminimizing these stresses can help, even the best managed lawns can suffer fromnematode damage from time to time.

If you are considering replanting your home lawn, and have had a history of nematodeproblems,choosing a different type of grass can sometimes help. Bahia grass is generally moretolerant of plant-parasitic nematodes than are other common lawn grasses and is oftena good choice, but even bahia grass may suffer under extreme nematode pressure ordrought conditions. Generally centipede grass is the only common lawn grass damagedby ring nematodes. Therefore, if you have a centipede grass lawn where ringnematodes have been problematic replanting with centipede grass might bea poor choice.

SummaryAt present, the best management strategies for nematodes in the home lawn are aimedat increasing the grass' ability to tolerate nematode damage. These strategies includeavoiding stress, promoting root vigor, and choosing tolerant grasses. Researchers atthe University of Florida are continually looking at new management options. Some ofthe options being investigated are testing of new safer products that are effective andcan be used on home lawns, screening of turfgrass varieties looking for betterresistance or tolerance to nematodes, and finding ways to use the nematodes' naturalenemies to suppress them below damaging levels.


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Table 1. Risk Levels for Warm-Season Turfgrasses used by the University of FloridaNematode Assay Laboratory.

NematodeSpecies Bermuda Zoysia Seashorepaspalum

St.Augustine

Centipede

M H M H M H M H M HRoot-knot(Meloidogyne)

80 300 80 300 80 300 80 300 80 300

Sting(Belonoaimus)

10 25 10 25 10 25 10 50 10 25

Lance(Hoplolaimus)

40 120 40 120 40 120 40 120 40 120

Stubby-root(Paratrichodorus)

150 300 150 300 150 300 150 300 150 300

Stubby-root(Trichodorus)

40 120 40 120 40 120 40 120 40 120

Spiral(Helicotylendhus)

700 1500 700 1500 700 1500 700 1500 700 1500

Spiral(Peltamigratus)

150 300 150 300 150 300 150 300 150 300

Ring(Mesocriconema)

500 1000 500 1000 500 1000 500 1000 150 300

Sheath(Hemicycliophora)

150 300 150 300 150 300 150 300 150 300

Sheathoid(Hemicriconemoides)

500 1000 500 1000 500 1000 500 1000 150 300

Awl(Dolichodorus)

10 25 10 25 10 25 10 25 10 25

Cyst(Heterodera)

--- --- --- --- --- --- 10 40 --- ---

Key:

--- = not believed to cause significant damage .

M = Turf is considered at moderate risk of damage. Damage may become evident if the turf is placed under stress conditions.H = Turf is considered at high risk of damage. Root systems are likely damaged and turf quality may be declining.

________________________________________________________________________________________________________* These risk levels are based upon numbers per 100 cc of soil extracted using a sugar-flotation with centrifugationmethod.

** While bahiagrass is a host for many of these nematodes, it is very tolerant to them and seldom is damaged.Therefore, no risk levels are given.


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*** Other nematodes such as dagger, lesion, stunt, etc. may damage turf in Florida, but damage from these is very rare so risklevels are not listed.**** These risk levels are based upon nematodes, grasses, and conditions in Florida only. They may not apply in other

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